The invention relates to improvements in apparatus for forming stacks of superimposed sheets or panels (hereinafter called panels), and more particularly to improvements in apparatus for forming stacks of coherent panels which are deposited on top of each other in zig-zag formation. Still more particularly, the invention relates to improvements in apparatus of the type wherein a continuous web of paper, metallic foil, plastic foil or other foldable material is or can be provided with transversely extending weakened portions to form fold lines which facilitate folding of neighboring panels relative to each other and wherein the web is or can be manipulated prior to stacking of successive foremost panels so that the panels form a scalloped stream or flow of partially overlapping coherent panels.
It is known to fold a web or strip of coherent panels so as to convert the web into a series of stacks which contain predetermined numbers of coherent panels in zig-zag formation. As a rule, neighboring panels of each stack are connected to each other by weakened fold lines which can contain rows of perforations so as to facilitate separation of neighboring panels from each other in a highly predictable fashion. Such panels are used in word processors and in similar machines and can bear printed matter so that each panel of the stack constitutes a form which can be filled out to constitute a shipping document, a completed questionnaire, a standard cover letter or any other document of a practically unlimited variety of documents which are used by government agencies and private firms. During folding of successive panels of the running web relative to the next-following panels, the panels are normally acted upon by suitable folding instrumentalities which ensure that the folding takes place only along fold lines and in such a way that the panels of the growing stack will pile up to constitute a zig-zag formation.
Problems arise when a conventional stack forming apparatus is called upon to make relatively tall stacks of overlapping panels in zig-zag formation. Thus, a tall stack of panels in zig-zag formation is likely to assume a shape which departs from an optimum form, especially that of a parallelepiped with neighboring sides disposed at right angles to each other. A predetermined shape is desirable for further processing of the stacks, particularly for wrapping and packing in boxes or in other types of receptacles.
One of the reasons that the shape of a relatively tall stack of superimposed panels in zig-zag formation is likely to depart from a predetermined optimum form is that those sides of the stack which are formed by the two rows of fold lines are taller than a section through the center of the stack between such sides. Thus, the central portion of the stack tends to be recessed or depressed (i.e., to sag) so that the panels of the stack are not flat but assume a concavo-convex shape. Each such stack is taller in the regions of the two rows of superimposed fold lines and is shorter in the regions between such sides. This not only interferes with further treatment (such as wrapping and boxing) of the stacks but also interferes with the operation of various components of the stack forming apparatus because such components are designed to operate properly when the shape of the growing stack matches an optimum shape.